Temperature-compensating device for electrical measuring instruments.



PATTNTED 1350.6 1904. W. H. BRISTOL. L

INSTRUMENTS. APPLUJTION FILED THB. 23. 19,04.

TEMPERATURE COMPENSATING DEVICE POR ELEGTRICALMEASURING No MoDBL.

' er n /1 Afro/awni-l WIT/VESSES:

Patented December 6, 1994.

UNITED' STATES -PATENT OFFICE.

WILLIAM H.v BRISTOL, .or Honolulu, NEW JERSEY.

TEMPERTUR-COM'PENSATING DEVICE FOR'ELECTRICAL MEASUR|NG` INSTRUMENTS.

SPECIFICATION for-'ming part of Letters Patent o. 776,491, dated becember 6, 1904. i

` Application led February 23, 1.904. Serial No. 194,839- (No model.) l

To al?, whom t may con/cern.:

Be it known that I, WILLIAM H. BRISTOL, a',l

citizen of the United States ofAmerica, residing at Hoboken, in the county of Hudson and State of New Jersey, have invented -certain new and useful Improvements inTemperature- Compensating Devices for Electrical Measur' ing Instruments, of specification.

My invention has reference to a device for automatically maintaining constante electrical resistance in a circuit for the purpose of obtaining accurate readings at the measuring inpensating device was more @rticularly in' tended for circuits of high electromotive force or voltage, while one ofthespecial objects ofmy present invention is to provide a device for automatically compensating for changes of resistance in the conductors leading -to'delicate electrical measuringinstruments-such, for instance, as millivoltmeters or other instruments for the measurements of currents of lowvoltage-such, for instance, as those produced by thermo-electric couples used individually or as part of pyrometers and like instruments.

With the abve object in view my invention consists, essentially, in the combination, with a measuring instrument having a low-resistance coil,.of a circuit, a conducting-column surrounding a portion of the circuit and adapted to shortqcircuit portions of said cir.- cuit with increase of temperature, and vice versa, it being understoodthat with ordinary metallic conductors the resistance increase with augmented temperature. My invention also consists in novel features in the construction of the temperature-com` pensating device and itsapplication to cirv cuits of high voltage.

The nature of my invention will be best which the following is a derstood when described connection withthe accompanying drawings, in which Figure 1 representsa diagrammatic view of an electrical apparatus to which vmy invention is applied.' Figs. 2, 3, 4, 5,- andillustrate different forms for the therm'ometric compensating device. v y Similar letters and numerals of reference` so` i designate corresponding parts throughout the severalviews of the drawings.

, Referring now to the drawings, the letter A designates a thermo-electricy couple or other source or generator of electricity supplylng a i -current o f low voltage.l

y B is the indicating, measuring, or recording device of a' usual construction, but pref erably provided with a `coil (not shown) of low resistance-say, for instance, one ohml instead of two hundred or more ohms, as usual in instruments of this character-thus rendering the instrumentextremely sensitive to slight changes in the electromotive force of the current.Y Under -ordinary circumstances such anV instrument is strongly iniuenced by chamgesv of resistance in the conductors due to variations in temperature, and its-readings are therefore unreliable.v l For the purpose of rendering such instruments-accurate I employ the compensating device (l, interpolated in the circuit from the generatorA in prox-` imity to tb e measuring instrument B. In Fig. 1 I have shown this compensating device to consist of a thermometer in the bulb 1, of*

which isfused or otherwise secured the terminal of one conductor 10, leading lfrom the generator A. In thebore of the thermometershank is arranged a rod, yvire, or `filament of equal or'higher resistance than the .generator-conductors andwhich ,is'placed in con.

nection with one of the binding-screws of the indicating, measuring, or'recording device B;

The lother binding-screw of the instrument B 90 is connected bythe conductor llwith the opposite pole of the-generator, as usual. The bulb of the thermometeris filled, as usual,

with a iiuid, such as mercury, oering a cross` section of high conductivity compared with that of the wire, rod, or filament 3. Ity w1ll Same.

readily be understood that as the mercury rises and falls with variations in temperature a corresponding portion of the wire, rod, or fila-ment will be short-circuited, or vice versa, thus decreasing or increasing the resistance in accordance with the length of the filament that is immersed, and so compensating for changes in temperature. It is of course to be understood that the resistance offered by the wire, rod, or filament is so calculated that the increments short-circuited correspond to the di'erence in resistance caused by increase of temperature.

While I have shown the end of the conductor attached to the bulb, and thelament, wire, or rod inserted' from the other end of the thermometer, it is of course to be understood that the conductor 10 could be passed directly through the thermometer and to the b inding-post at the measuring instrument B without a break.

In Figs. 2 and 3 I have shown/the wire, rod, or filament in the form of a loop entering the shank of the thermometer and having the two members separated from each other by an insulating-partition 5, of glass or other suitable material, to prevent contact of the The free ends of the loop are attached, respectively, to one pole of the generator A and to one binding-post of the measuring instrument. It will be readily understood that with this construction twice the amount of the wire, rod, or filament 3 will be thrown in or cut out with the same variation of the column of mercury in the compensating device shown in Fig. l. In Fig. 4 I have shown the insulating-partition in the form of a tube 6, surrounding one of the members of the loop.

When it is desired to throw in or out a large resistance with a comparatively small change in the height of the mercurial column, I make use of the construction shown in Figs. 5l and 6. In this construction the body of the thermometer is provided with a bulbl of considerable length and width, and the shank is formed to correspond, thus permitting the insertion of al coil 7 into the shank. This coil may consist of a large number of windings or convolutions about a core 8 of non-conducting material-such, for instance, asY mica-so as to insulate the windings from each other. The terminals of the coil are connected, as before, with one pole of the generator and with one binding-post of the measuring instrument. In practice-I prefer to make the body of the thermometer of metal, and therefore make use of means for insulating the coil from the walls thereof. This is best accomplished by the use of m'ica plates 9, attached to'the core 8. The top of the thermometer-body can be hermeticall y sealed by a suitable cap 12 in the usual manner. Of course ifv the thermometerbody is made of glass the additionalA .side insulation is not necessary.

While I have herein described the compen sating device as more particularly adapted for instruments of low resistance, it can be applied to voltmeters of usual construction to compensate all variationsin temperature.

It will be noticed that one of the main'fea# tures of my present invention is to compensate perfectly without materially increasing the resistance of the circuit.

1. In combination with agenerator of electricity and a measuring instrument having 'a low-resistance coil, a temperature-com pensating device located iny proximity to the measuring instrument and containing a mercuric column acting on a resistance in series in the circuit Jr'or automatically maintaining constant the total resistance of the part of the circuit comprising the measuring instrument and the compensating device under variations in temperature. i

2. In combination with a source of current and a measuring instrument, an electrical temperature-compensating device included in series in the circuit and located in proximity to the measuring instrument, the said compensating device consisting of a resistance in a liquid thermometric device automatically maintaining constant the total resistance of the part of the circuit comprised by the measuring instrument and the compensating device under variations in temperature.

3. In combination with a source of current and a measuring instrument, an electrical temperature-compensating device included in series in the circuit and located in proximity t0 the measuring instrument, the said compensating device consisting of a resistance in a mercurial thermrnetric device automatically maintaining constant the total resistance of the part of the circuit comprised by the measuring instrument and the compensating device during variations in temperature.

4. In combination with a'generator of electricity and a measuring instrument, a mercurial temperature-compensating device located in proximity to the measuring instrument and having a portion of one of the conductors from the generator passing therethrough and placed in communication with the measuring instrument, whereby the tot'al resistance of the part of the circuit comprised by the measuring instrument and the compensating instrument is maintained substantially constant Aby'iiuctuations in the column of mercury.

5. In combination with a source of current and a measuring instrument, v'an electrical tem'- perature-compensating device in series in the circuit and located in 'proximity to themes-suring instrument, the said compensating device consisting of a liquid thermometer having in its shank alooped resistancegwire, rod or filament.

6. In -combination with a source of current IIO and a measuring instrument, an electrical temperature-compensating device including in series in the circuit andloeated in proximity to the measuring instrument, the said compensating device consisting of aliquid thermometer having in its shank a looped resistance Wire, rod or lament, and means for insulating the wires, rods or filaments from each other.

7 In combination With a source of current and a measuring instrumen t, an electrical temperatu re-compensating device including in series in the circuit and located in proximity to the measuring' instrument, the said compensating device consisting of a liquid thermometer having in its shank a looped resistance wire, rod or filament, means for insulating the wires, rods or laments from each other, and means for insulating the same from the body of the thermometer.-

8. In combination with a source of current and a measuring instrument, an electrical temperature-compensating device including in series in the circuit and located in proximity to my hand in the perature-compensating device including in series in the circuit and located in proximity to the measuring instrument, the said compening itslshank of elongated or fiattened form 35 sating device consisting of a thermometer havtransversely and a resistance-coil of iattened form inserted in said shank combined with'a mercurial column.

In testimony whereof I have hereunto set witnesses.

WILLIAM H. BRISTOL.

IWitnesses: l

A. FABER nu FAUR, Jr., RAENA H. YUDIZKY.

presence of two subscribing 

